1. Field of the Invention
The present invention is directed to a copolymer of vinylene carbonate and 1-olefins, a process of forming that copolymers, and packaging films containing such polymers.
2. Background of the Invention
Previously reported methods of copolymerizing vinylene carbonate and 1-olefins have been directed to free-radical initiated polymerizations normally carried out at elevated temperature and pressures of greater than about 1000 atm. Such conditions have required the use of, inter alia, elaborate high pressure reactors. See, e.g., R. A. Terteryan et al., Vysokomol. Soedin., 8(10), 1721-1726 (1966) (polymerization using azobisisobutyronitrile as free-radical initiator at elevated temperature and pressure) and S. M. Samoilov et al., USSR Plast. Massy, Issue 7, 15-17 (1969) (ethylene-vinylene carbonate copolymers prepared under high pressure conditions having a significant amount of short and long chain branches reportedly could be formed into films, although such branched copolymers generally have properties inferior to those of copolymers having similar composition but a linear architecture).
Other modes of catalytic polymerization, such as those using conventional Ziegler-Natta type catalysts or cationic Group IV metal catalysts, have not produced desired copolymers due to the corrupting effect of vinylene carbonate on such catalyst systems.
Using .gamma. irradiation to graft vinylene carbonate onto the surface of previously formed low density polyethylene (LDPE) films, with an accompanying improvement in hydrophilic properties, is described in, e.g., G. Chen et al., J. Appl. Poly. Sci., 45(5) 853-864 (1992). This technique produces a copolymer distinct from those described above in which the vinylene carbonate is part of the backbone chain of the copolymer.
Producing vinylene carbonate/1-olefin copolymers that are substantially linear and exhibit low polydispersity remains highly desirable. Copolymers having significantly fewer branches can have properties superior to those of copolymers formed by conventional free-radical processes such as, e.g., processing into packaging films and other articles. Further, a process that can produce such copolymers under low temperature and low pressure conditions, which can reduce demand on the needed equipment, also remains desirable.